Method of and apparatus for using a geothermal power plant

ABSTRACT

A transportation system is based on battery powered vehicles operating in an isolated geographic area within which a base electrical load during the day exceeds the normal electrical load during the night. The system is operated by generating power for the load by using a geothermal power plant that operates day and night at a substantially constant power output. The vehicles are operated during the day; and power generated by the power plant supplies the base electrical load. Recharging of the batteries of the vehicles occurs only at night when power generated by the power plant in excess of the normal electrical load is available for recharging purposes.

RELATED APPLICATION

This application is a continuation of application Ser. No. 08/768,272filed Dec. 18, 1996 (now U.S. Pat. No. 5,740,672 which issued Apr. 21,1998), which is a continuation of application Ser. No. 08/000,551 filedJan. 4, 1993 (now abandoned), which is a continuation of applicationSer. No. 07/656,879 filed Feb. 19, 1991 (now abandoned).

TECHNICAL FIELD

This invention relates to methods for using a geothermal power.

BACKGROUND OF THE INVENTION

In many parts of the world, isolated land masses exist which require theimportation of fossil fuels to generate electrical power. The HawaiianIslands are an example of such land masses; and power generation ispresently limited to conventional fossil-fueled plants using steam orgas turbines which produce undesirable atmospheric pollutants. In aneffort to improve the environment, it has been proposed to utilizegeothermal sources to produce power. If the geothermal sources arepresent on certain outlying islands, the power produced can be sent tothe main islands, for example, by conventional underwater powertransmission lines. Because the normal electrical load in the islands issuch that the load during the day or periods of peak power demandgreatly exceeds the load at night, or during periods of off-peak powerdemand, geothermal power plants inherently are not totally suitable. Theproblem is that a geothermal power plant usually operates at ratedcapacity all the time, both day and night. Thus, a plant capable ofsupplying the daytime load would have excess capacity at night. Becauseof the geographical isolation of the plant, it is not practical totransmit the excess power produced at night to another customer; and forthis reason, large scale geothermal power plants are often notappropriate for the conditions described above. Consequently,conventional fossil-fueled power plants are supplemented by faststarting gas turbine power units for daytime peaking because these unitscan be brought on and off line quickly. Generating electricity usingconventional oil-fired plants using steam turbines for base line powerproduction supplemented by gas turbine peaking is both expensive andpolluting.

Geothermal power plants are cost effective, but the nature of theseplants is not conducive to quickly starting and stopping, which meansthat the substitution of such plants for conventional fossil-fueledplants is not practical in a geographically isolated location whereexcess power at night cannot be disposed of. One approach to thisproblem is to vent the geothermal production wells at night, and reducethe operating level of the plant to accommodate the low level loadduring the night. This approach is not desirable because geothermalvapors contain noxious gases which, when released to the atmosphere, aredangerous to human health. Treatment systems exist for removing noxiousgases, but the cost of this equipment is prohibitive. It is therefore anobject of the present invention to utilize a geothermal power plant in anew and different way so as to avoid the problems with the prior art asoutlined above.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a method for operating a transportationsystem based on electric powered vehicles, such as battery poweredvehicles particularly suitable for use in an isolated geographic areawithin which the base electrical load during the day, or periods of peakdemand, exceeds the normal electrical load during the night, or periodsof off-peak power demand. The method includes the steps of generatingpower for the electrical load wherein a power production system or ageothermal power plant that operates day and night, preferably atsubstantially constant power output, may be used or included in thepower production system. Thus, for example, during the day, the powerplant supplies the required electrical load, and the battery poweredvehicles are operated without imposing any load on the power plant. Thisis particularly effective when the geographical area served by the powerplant is isolated, and vehicular traffic is essentially tourist travel.

During the night, the batteries of the vehicles are charged utilizingthe power generated by the power plant at night in excess of the normalelectrical load. Thus, the electrical load supplied, for example, by thegeothermal power plant during the day is the usual daytime load, and theelectrical load supplied by the geothermal power plant during the nightis the normal nighttime load plus the load imposed by recharging thebatteries in the vehicles.

Preferably, recharging stations are provided in the geographic area arelinked by roads over which the battery powered vehicles travel.Advantageously, the distance between adjacent stations can be selectedso as to be substantially equal to the cruising range of a vehicle whichmeans that a vehicle can travel from one station to the next station ona full battery charge. Such travel occurs during the day so that, atnight, the vehicle may be recharged at a charging station.

The invention also consists of a transportation system for an isolatedgeographic area comprising a ring-road defining the geographical area,and a plurality of re-charging stations spaced around the ring-road. Anelectrical distribution system is provided for supplying power to therecharging stations wherein the electrical distribution system mayinclude a geothermal power plant that preferably produces power at asubstantially constant rate.

Thus, the increased electric load during periods of off-peak powerdemand, such as during the night, will lead to increased use ofgeothermal power plants, usually increasing the level of powerproduction of such plants thereby reducing the amount of pollutantsproduced in electric power production. Also, the use of battery operatedcars will bring about a reduction in air pollution because the number offossil fueled cars or vehicles will be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described below by way ofexample and with reference to the accompanying drawings wherein:

FIG. 1 is a schematic plan of an isolated geographic area comprising anisland similar to one of the Hawaiian Islands showing a transportationsystem including a geothermal power plant in accordance with the presentinvention;

FIG. 2 is a further schematic plan of an isolated geographic areacomprising two islands similar to the Hawaiian Islands showing atransportation system in accordance with the present invention;

FIG. 3 is a schematic block diagram of a battery operated vehicleshowing the manner in which recharging is achieved; and

FIG. 4 is a schematic block diagram of a geothermal power plant shownschematically in FIG. 1.

DETAILED DESCRIPTION

Referring now to the drawings, FIG. 1 illustrates a transportationsystem based on battery powered vehicles in an isolated geographic areawithin which a base electrical load during the day exceeds the normalelectrical load during the night. As shown in FIG. 1, island 40preferably is provided with geothermal power plant 10 and electricalsubstation 41, or other power plant facilities, providing power totransmission line 46. On island 40 is ring-road 44 which generallyfollows the shoreline of the island completely therearound. Transmissionline 46 which circles the island, generally follows ring-road 44.

Located at several different locations on ring-road 44 are rechargingstations 47 which, preferably, are equidistant apart. The distance maybe chosen to be compatible with the cruising range of battery poweredelectrical vehicles 48. Stations 47 tap into transmission line 46. Ifpreferred, a bank of, or several, charged batteries, can be provided ormade available at the various stations to enable an operator to exchangea discharged battery from a car with a charged battery.

If the geothermal power plant is located on another island outlying themain island, geothermal power plant 10 together with substation 41 maybe located on the outlying island indicated by reference numeral 43 inFIG. 2. As shown in FIG. 2, substation 41 provides power to transmissionline 42 connected to main island 40 and terminates at substation 45which supplies power to land based transmission line 46.

As shown in FIG. 3, each vehicle 48 includes chassis 49 on which aremounted electric motor 50 and transmission 51 for the purpose of drivingwheels 52. Also mounted on chassis 49 is storage battery 53 whichprovides power for motor 50 by way of control means 54 which is operatedby a user.

Associated with battery 53 is charge level detector 55 for the purposeof determining the charge level on the storage batteries. Control 54 isresponsive to the charge level detector for operating alarm 56 when thecharge level falls to a threshold.

Preferably, each car is provided with a communication system, such as atelephone, which can also be used to communicate with the rechargingstation. Furthermore, advantageously, emergency vehicles may be locatedat one or more of the various recharging stations for providing service,for example, delivering batteries to a vehicle or to a station as theneed may arise.

In operation, vehicles 48 preferably would be made available during theday with a full battery charge at a recharging station. The user couldthen travel to the next recharging station during the day depleting thecharge on the battery. The capacity of the battery and the design of thevehicle is such that the cruising distance and speed are such thattransit from one station to the next takes a reasonable time, say nomore than 4 hours. Alternatively, the vehicles could be used in thevicinity of a charging station, and returned there at night forrecharging. This arrangement is particularly well suited to car rentals.

The resultant increased electric load during periods of off peak powerdemand, such as during the night, in order to charge batteries, willlead to increased use of geothermal power plants, usually by increasingthe level of power production from such plants. This will reduce theamount of power produced by conventional fossil-fueled power plantsleading to a reduction in pollutants by such plants. In addition, theuse of battery operated vehicles will further reduce air pollution as aresult in a reduction in the number of fossil fueled vehicles used.

Even though the above description refers to a geothermal power plantindicated by reference numeral 10 in FIGS. 1 and 2, as preferablyproducing substantially constant power continuously during the day andthe night, the present invention also contemplates the use of a modulargeothermal power plant where, if necessary, one or more modular unitscan be used to produce power. Such a geothermal power plant is describedin U.S. patent application Ser. No. 444,565 filed Dec. 1, 1989 (now U.S.Pat. No. 5,497,624 issued Mar. 12, 1996), the disclosure of which ishereby incorporated by reference. The '624 patent discloses a powerplant module for producing electric power from a source of geothermalfluid that produces steam containing non-condensable gases and brine.The module includes a steam turbine operating on steam from the sourceof geothermal fluid for producing power and heat depleted steam, a steamcondenser for receiving the heat depleted steam, and means forindirectly cooling the steam condenser with liquid organic fluid therebyproducing vaporized organic fluid and steam condensate. The power plantalso includes an organic vapor turbine operating on the vaporizedorganic fluid for producing power and heat depleted organic vapor, anorganic fluid condenser for condensing the heat depleted organic vaporinto liquid organic fluid, and a pump for returning the organic liquidto the steam condenser. Finally, the power plant also includes apreheater for preheating the organic liquid, before it is supplied tothe steam condenser, with heat present in the geothermal fluid andcontained in fluid or brine derived from the geothermal fluid. Theutilization of such a power plant increases its flexibility bypermitting a reduction of power by removing one or more modules from theline. This is particularly advantageous during maintenance periods. Evenin such a modular geothermal power plant, its use will lead to areduction in air pollution.

The advantages and improved results furnished by the method andapparatus of the present invention are apparent from the foregoingdescription of the preferred embodiment of the invention. Variouschanges and modifications may be made without departing from the spiritand scope of the invention as described in the appended claims.

What is claimed is:
 1. A system for an isolated geographic area such asan island having a source of geothermal fluid that produces steamcontaining non-condensable gases, and brine, said system comprising: a)a plurality of battery operated vehicles for traversing said area, eachvehicle being provided with a battery, a charge level detector fordetermining the charge level on said battery, an alarm, and controlmeans for operating the alarm when the charge level on said batteryfalls to a threshold; b) a plurality of charging stations located insaid area for recharging the batteries of said vehicles; c) anelectrical grid for distributing power to said geographical area whichrequires more power during the day than at night; and d) a geothermalpower plant for supplying power to said grid at a substantially constantpower level day and night, said power plant including at least onemodule comprising: (1) a steam turbine operating on steam from thesource of geothermal fluid for producing power and heat depleted steam;(2) a steam condenser for receiving the heat depleted steam; (3) meansfor indirectly cooling the steam condenser with liquid organic fluidthereby producing vaporized organic fluid and steam condensate; (4) anorganic vapor turbine operating on the vaporized organic fluid forproducing power and heat depleted organic vapor; (5) an organic fluidcondenser for condensing the heat depleted organic vapor into liquidorganic fluid; (6) means for returning said organic liquid to the steamcondenser; and (7) a preheater for preheating the organic liquid, beforeit is supplied to said steam condenser, with heat contained in thegeothermal fluid.
 2. A system according to claim 1 wherein saidgeographic area is an island.
 3. A system according to claim 1 includingmeans for supplying said brine to said preheater for producing cooledbrine.
 4. A system according to claim 1 wherein said organic fluid ispentane.
 5. A system according to claim 1 wherein a single electricgenerator is interposed between and individually driven by the steamturbine and the organic vapor turbine.
 6. A system according to claim 1including means for supplying said steam condensate to a re-injectionwell.
 7. A system according to claim 1 wherein non-condensable gasescollect in said steam condenser, and including means for compressingsaid non-condensable gases, and means for supplying the compressednon-condensable gases to a re-injection well.
 8. A system according toclaim 7 including means for supplying said steam condensate to saidre-injection well.
 9. A system according to claim 7 including means foradding brine to said steam condensate prior to combining the compressednon-condensable gases with the steam condensate.
 10. A system accordingto claim 9 including means for supplying steam condensate, brine andcompressed non-condensable gases to the same re-injection well.
 11. Asystem according to claim 3 including means for supplying said cooledbrine to a re-injection well; and means for compressing non-condensablegases which collect in said steam condenser, and means for supplying thecompressed non-condensable gases to a re-injection well.
 12. A systemaccording to claim 1 including means for supplying liquid derived fromsaid geothermal fluid to said preheater for supplying heat contained insaid geothermal fluid.
 13. A system according to claim 12 wherein saidliquid derived from said geothermal fluid is said brine.
 14. A systemaccording to claim 12 wherein said power plant is located on a separateisland.
 15. A system for an isolated geographic area such as an island,said system comprising: a) a plurality of battery operated vehicles fortraversing said area, each vehicle being provided with a battery, acharge level detector for determining the charge level on said battery,an alarm, and control means for operating the alarm when the chargelevel on said battery falls to a threshold; b) a plurality of chargingstations located in said area for recharging the batteries of saidvehicles; c) an electrical grid for distributing power to saidgeographical area which requires more power during the day than atnight; and d) a geothermal power plant operating from a source ofgeothermal fluid for supplying power to said grid at a substantiallyconstant power level day and night, said power plant including at leastone module comprising: (1) a heat exchanger for indirectly cooling fluidderived from said geothermal fluid with liquid organic fluid therebyproducing vaporized organic fluid and cooled fluid; (2) an organic vaporturbine operating on the vaporized organic fluid for producing power andheat depleted organic vapor; (3) an organic fluid condenser forcondensing the heat depleted organic vapor into liquid organic fluid;(4) means for returning said organic liquid to the heat exchanger; and(5) a preheater for preheating the organic liquid, before it is suppliedto said heat exchanger, with heat contained in the geothermal fluid. 16.A system according to claim 15 wherein said geographic area is anisland.
 17. A system according to claim 15, wherein said geothermalfluid produces brine which is supplied to said preheater for preheatingthe organic liquid with heat contained in the geothermal fluid beforethe organic fluid is supplied to said heat exchanger and producingcooled brine.
 18. A system according to claim 15 wherein said organicfluid is pentane.
 19. A system according to claim 17 including means forsupplying said cooled brine to a re-injection well.
 20. A systemaccording to claim 15 including a steam turbine operating on steam fromsaid source of geothermal fluid, and wherein said fluid derived fromsaid geothermal fluid comprises steam condensate exiting said steamturbine.
 21. A system according to claim 15 wherein said power plant islocated in a further isolated geographic area separate from saidgeographic area.
 22. A system for an isolated geographic area such as anisland, said system comprising: a) a plurality of vehicles fortraversing said area, each vehicle being provided with an electricallyoperated motor; b) an electrical grid for distributing power to saidgeographical area which requires more power during the day than atnight; and c) a geothermal power plant operating from a source ofgeothermal fluid for supplying power to said grid at a substantiallyconstant power level day and night, said power plant including at leastone module comprising: (1) a heat exchanger for indirectly cooling fluidderived from said geothermal fluid with liquid organic fluid therebyproducing vaporized organic fluid and cooled fluid; (2) an organic vaporturbine operating on the vaporized organic fluid for producing power andheat depleted organic vapor; (3) an organic fluid condenser forcondensing the heat depleted organic vapor into liquid organic fluid;(4) means for returning said organic liquid to the heat exchanger; and(5) a preheater for preheating the organic liquid, before it is suppliedto said heat exchanger, with heat contained in the geothermal fluid. 23.A system according to claim 22 wherein said geographic area is anisland.
 24. A system according to claim 22 wherein said geothermal fluidproduces brine which is supplied to said preheater for preheating theorganic liquid with heat contained in the geothermal fluid before theorganic fluid is supplied to said heat exchanger and producing cooledbrine.
 25. A system according to claim 22 wherein said organic fluid ispentane.
 26. A system according to claim 24 including means forsupplying said cooled brine to a re-injection well.
 27. A systemaccording to claim 22 including a steam turbine operating on steam fromsaid source of geothermal fluid, and wherein said fluid derived fromsaid geothermal fluid comprises low pressure steam exiting said steamturbine.
 28. A system according to claim 22 wherein said power plant islocated in an isolated geographic area separate from said geographicarea.
 29. A system according to claim 22 wherein said plurality ofvehicles provided with an electrically operated motor comprises aplurality of vehicles including motors having a battery.
 30. A systemaccording to claim 29 wherein said plurality of vehicles including amotor having a battery comprises a plurality of vehicles each of whichis provided with a battery, a charge level detector for determiningcharge level on the battery, an indicator, and control means foroperating the indicator when the charge level on the battery falls to athreshold.
 31. A system according to claim 30 wherein said plurality ofvehicles including a motor having a battery comprises a plurality ofvehicles, each having a battery operated motor.
 32. A system accordingto claim 30 including a plurality of charging stations located in saidarea for recharging the batteries of said vehicles.
 33. A method foroperating a transportation system for an isolated geographic area suchas an island comprising: a) providing a plurality of battery operatedvehicles for traversing said area, each vehicle being provided with abattery, a charge level detector for determining the charge level onsaid battery, an alarm, and control means for operating the alarm whenthe charge level on said battery falls to a threshold; b) providing aplurality of charging stations located in said area for recharging thebatteries of said vehicles; c) providing an electrical grid fordistributing power to said geographical area which requires more powerduring the day than at night; and d) providing a geothermal power plantoperating from a source of geothermal fluid for supplying power to saidgrid at a substantially constant power level day and night, said powerplant including at least one module comprising: (1) a heat exchanger forindirectly cooling fluid derived from said geothermal fluid with liquidorganic fluid thereby producing vaporized organic fluid and cooledfluid; (2) an organic vapor turbine operating on the vaporized organicfluid for producing power and heat depleted organic vapor; (3) anorganic fluid condenser for condensing the heat depleted organic vaporinto liquid organic fluid; (4) means for returning said organic liquidto the heat exchanger; and (5) a preheater for preheating the organicliquid, before it is supplied to said heat exchanger, with heatcontained in the geothermal fluid.
 34. A method according to claim 33including operating the transportation system for an isolated geographicregion on an island.
 35. A method according to claim 33 includingproducing brine from said geothermal fluid and supplying said brine tosaid preheater for preheating the organic liquid with heat contained inthe geothermal fluid before the organic fluid is supplied to said heatexchanger and producing cooled brine.
 36. A method according to claim 33wherein the step of providing a geothermal power plant operating from asource of geothermal fluid including at east one module is carried outby providing at least one module operating on pentane.
 37. A methodaccording to claim 35 including supplying said cooled brine to are-injection well.
 38. A method according to claim 33 includingproviding a steam turbine operating on steam from said source ofgeothermal fluid, and wherein said fluid derived from said geothermalfluid comprises low pressure steam exiting said steam turbine.
 39. Amethod according to claim 33 including locating said power plant in afurther isolated geographic area separate from said geographic area. 40.A method for operating a transportation system for an isolatedgeographic area such as an island, comprising: a) providing a pluralityof vehicles for traversing said area, each vehicle being provided withan electrically operated motor; b) providing an electrical grid fordistributing power to said geographical area which requires more powerduring the day than at night; and c) providing a geothermal power plantoperating from a source of geothermal fluid for supplying power to saidgrid at a substantially constant power level day and night, said powerplant including at least one module comprising: (1) a heat exchanger forindirectly cooling fluid derived from said geothermal fluid with liquidorganic fluid thereby producing vaporized organic fluid and cooledfluid; (2) an organic vapor turbine operating on the vaporized organicfluid for producing power and heat depleted organic vapor; (3) anorganic fluid condenser for condensing the heat depleted organic vaporinto liquid organic fluid; (4) means for returning said organic liquidto the heat exchanger; and (5) a preheater for preheating the organicliquid, before it is supplied to said heat exchanger, with heatcontained in the geothermal fluid.
 41. A method according to claim 40including operating the transportation system for an isolated geographicarea on an island.
 42. A method according to claim 40 includingproducing brine from said geothermal fluid and supplying said brine tosaid preheater for preheating the organic liquid with heat contained inthe geothermal fluid before the organic fluid is supplied to said heatexchanger and producing cooled brine.
 43. A method according to claim 40wherein the step of providing a geothermal power plant operating from asource of geothermal fluid including at least one module is carried outby providing at least one module operating on pentane.
 44. A methodaccording to claim 42 including supplying said cooled brine to are-injection well.
 45. A method according to claim 40 includingproviding a steam turbine operating on steam from said source ofgeothermal fluid, and wherein said fluid derived from said geothermalfluid comprises low pressure steam exiting said steam turbine.
 46. Amethod according to claim 40 including locating said power plant in anisolated geographic area separate from said geographic area.
 47. Asystem according to claim 40 wherein the step of providing saidplurality of vehicles provided with an electrically operated motor iscarried out by providing a plurality of vehicles including motors havinga battery.
 48. A method according to claim 47 wherein the step ofproviding said plurality of vehicles including a motor having a batteryis carried out by providing a plurality of vehicles each of which isprovided with a battery, a charge level detector for determining chargelevel on the battery, an indicator, and control means for operating theindicator when the charge level on the battery falls to a threshold. 49.A method according to claim 48, wherein the step of providing saidplurality of vehicles including a motor having a battery is carried outby providing a plurality of vehicles, each vehicle having a batteryoperated motor.
 50. A method according to claim 48 including providing aplurality of charging stations located in said area for recharging thebatteries of said vehicles.